Millions of acres of farmland in the U.S. have been affected by herbicide-resistant weeds, rendering some fields unable to be farmed. And the problem is spreading, which could mean more lost crops and lost profits. The EPA approved a new herbicide to be used with USDA-approved genetically modified seeds, but opponents have sued, warning it could harm the environment and human health. NewsHour Weekend's Megan Thompson reports.​

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MEGAN THOMPSON:

Autumn means it's harvest time in Iowa, the heart of America's Heartland. Farmer Jeff Jorgenson is busy harvesting soybeans. He also grows corn on about 2,000 acres in the southwest corner of the state.

Farming is big business here in Iowa. This state is the biggest producer of corn in the country. And it's second only to Illinois in the production of soybeans.

For Jorgenson – whose family's been farming for four generations – it's all about keeping his yields as high as he can.

JEFF JORGENSON:

Yield monitor's here.

MEGAN THOMPSON:

And one of the biggest battles he fights is against weeds.

JEFF JORGENSON:

A weed in the field's going to take moisture, going to take sunlight, nutrients away from the plants surrounding it. And that's why we have to keep clean fields.

MEGAN THOMPSON:

But Jorgenson says, keeping "clean" fields has been getting harder and harder. Like many farmers, he relied for years mainly on an herbicide called "Roundup" that's manufactured by Monsanto.

Roundup use exploded in the mid-90's with the introduction of new genetically modified crops that dominate the market today. The crops were engineered to withstand Roundup. So farmers could just spray an entire field, and the herbicide would kill the weeds, but not the crops.

JEFF JORGENSON:

Any weed you had in the field, Roundup took care of. Roundup revolutionized weed management for farmers.

MEGAN THOMPSON:

Jorgenson says it all worked great, for awhile. He no longer had to spend lots of time plowing to kill weeds. But over time, Roundup and its generic versions – all of which contain a chemical called glyphosate – stopped working so well.

MIKE OWEN:

Simple use of one herbicide recurrently in the system is going to inevitably result in weeds that evolve resistance to that herbicide.

MEGAN THOMPSON:

Agronomy professor Mike Owen is a nationally-recognized weed expert at Iowa State University in Ames.

MIKE OWEN:

It is a widespread and- and is significant from an economic perspective problem across the Midwest and, dare I say, across agriculture in general.

MEGAN THOMPSON:

Owen says it's no mystery why this happened – it can all be explained by evolution. In Iowa, one of the weeds that's evolved to be resistant is called "waterhemp."

JEFF JORGENSON:

This is giant waterhemp, a weed we have down in southwest Iowa that's become more tolerant. This plant, when it's mature, will be, can get 5 to 6 feet tall, where it's very heavy, you can have yields cut in half, 50 percent losses.

MIKE OWEN:

In Iowa, we would estimate as that about 75 percent of the fields have infestations of common waterhemp that are resistant to one or more herbicides.

MEGAN THOMPSON:

The weeds are not just a problem in Iowa. In one survey, almost 50 percent of farmers across the U.S. reported herbicide-resistant weeds in their fields. The problem is worst in the south, where some cotton fields can't be farmed. But the threat is creeping north into the corn and soybean belts. Keep in mind, crop yields in the U.S. are booming. But Mike Owen says it's possible they could be even higher were it not for the weeds. Owen says it's difficult to quantify the damage. But if the weeds start having a significant impact, it could be too late.

MIKE OWEN:

We have, if you will, hidden yield losses and thus hidden profit losses on millions and millions of acres in the Midwest. It hasn't gotten to the point, if you will, of the train wreck.

MEGAN THOMPSON:

What could happen, or what's at stake if this doesn't get under control?

MIKE OWEN:

Well, the train wreck. And- and that is the inability to produce crops.

MEGAN THOMPSON:

Over the last four years, the issue started to get more and more attention. Congress held hearings… and the USDA recently announced new measures it's taking to combat the problem…. A problem also acknowledged by Monsanto. And now another major manufacturer has stepped in.

PROMOTIONAL VIDEO:

Growers across the country face an increasing problem from resistant and hard-to-control weeds.

MEGAN THOMPSON:

Biotech giant Dow Agrosciences recently won federal approval for new genetically modified corn and soybeans, and a new herbicide to go with them called Enlist Duo. Dow is promoting it as an answer to the herbicide-resistant weed problem.

PROMOTIONAL VIDEO:

These weeds are out of control.

MEGAN THOMPSON:

But there's another piece to all of this. And that is, whether the herbicides used to control weeds pose health risks for farmers and the rest of us. The center for food safety, a national environmental advocacy group, recently sued the EPA, alleging the agency didn't fully analyze the new herbicide's potential effects on human health and the environment.

MEGAN THOMPSON:

The group cites studies that suggest a correlation between pesticides and diseases like Non-Hodgkin lymphoma and Parkinson's. Attorney Andrew Kimbrell heads the Center for Food Safety.

ANDREW KIMBRELL:

They're bad for us, right, because it's going to mean much more of these toxic herbicides in our food, in our groundwater, in the air.

MEGAN THOMPSON:

But in approving the product, the EPA published this document saying its scientists determined: "when used according to label directions, Enlist Duo is safe for everyone, including infants, the developing fetus, the elderly and more highly exposed groups such as agricultural workers."

MEGAN THOMPSON:

In a statement to the NewsHour, Dow quoted the EPA analysis. And added, its new system helps farmers "as they struggle to control weeds that impact the food supply, while respecting the well being of both people and the environment."

The EPA approved the new product for use only in six states so far. And it imposed restrictions: 30-foot buffer zones, no aerial spraying, and no applications in windy conditions. The new product is a mix of the main ingredient in Roundup – glyphosate – and a chemical called 2,4-D – used for decades and found in many common lawn care products.

MEGAN THOMPSON:

Pretty much anybody can walk into a hardware store and buy a product for use on their lawn that contains this stuff. So, if it's so dangerous, why is it so widely available?

ANDREW KIMBRELL:

This isn't just about 2,4-D. Enlist Duo, the product that's been approved, is also glyphosate. What do they mean together? We know some of the health impacts separately, but what happens when they're- when they come together and- and combine? What does that actually mean for health effects? What does it mean for toxic effects on farmers and applicators?

MIKE OWEN:

We have the model system with the EPA reviewing the safety of these herbicides and my sense is that the evidence says that the herbicides when used appropriately are safe.

MEGAN THOMPSON:

But even if they are safe, there are serious concerns that weeds could become resistant to the new herbicide, just as they did to Roundup. It's something the EPA is requiring Dow to monitor.

MIKE OWEN:

The problem will inevitably get worse unless changes are made.

MEGAN THOMPSON:

Changes like relying less on chemicals. And also going back to some of the old ways – like growing crops in the offseason to suppress weeds … and removing some weeds mechanically.

MIKE OWEN:

Growers thus far have been wanting a new, simple solution. And unfortunately, the industry has not been able to come up with, if you will, another silver bullet.

MEGAN THOMPSON:

Farmer Jeff Jorgenson says he thinks the new Dow products – expected to come to market this spring – will help farmers, especially in the south. To battle his weeds, he's been mixing other herbicides in with Roundup, something Monsanto recommends. But, Jorgenson says he knows his system will inevitably have to evolve … just like the weeds.

MEGAN THOMPSON:

Are you afraid that your system might stop working?

JEFF JORGENSON:

Oh, there's no question. It will change. There will be a time where it will not have the effect that it does now. After seeing what's happened with Roundup, you always have the worry that whatever chemical program you're using what will happen if it loses its effectiveness. That is always on farmers' minds because we need to be able to control the problems that we have in fields.